1. Field of the Invention
The present invention relates to a printing apparatus provided with detection means for detecting the amount of mechanical movement, and capable of effecting the printing operation according to a signal from the detection means.
2. Description of the Prior Art
In general, a printer performs printing operation by the movement of certain mechanical elements, such as a carriage or a type font wheel. There is already known a printer capable of detecting the movement of such elements and prohibiting the printing operation in case of an abnormality in the movement.
FIG. 1 illustrates an example of a printer, for electronic apparatuses, in which the printing operation is effected by a type font belt, and in which each type on the belt is detected by mechanical detection means composed of encoding plates 15, 16 and metal contactors 12a, 13a. Such printer may generate an error in the type detecting operation, for example due to an incomplete contact in the detection means, thus providing an erroneous print.
In order to avoid such error, there has been employed so-called error lock structure, in which the type detecting operation is conducted by circulating the type font belt by one cycle at a determined timing, for example at the end of each print line, and the data processing, data output for recording and data input from keyboard are prohibited in case an error is identified in the detection.
Such error lock function is provided for informing the operator of a disabled state for proper printing operation, and is indispensable for an electronic apparatus equipped with a printer in which the types of the type font wheel are detected by mechanical detection means as explained above.
It is already confirmed that the errors in the function of such type detection means are most frequent at the start of power supply after the printer has been left unused for a prolonged period, and become quite rare thereafter.
Therefore, in the conventional structure in which the error lock function is activated even for an error detected at the start of power supply, the error lock function is activated often at the start of power supply so that the operator is required to execute a procedure for cancelling such error lock state, such as the actuation of a clear key "C".
On the other hand, the prevention of a detection error at the start of supplying power requires a measure involving an additional cost, such as the application of special oil to the detection mechanism, in order to ensure complete function of the type detection means even at the start of supplying power.